1. Field of the Invention
The present invention relates to a method and an apparatus of detecting convexity on surfaces of various belt-shaped and roll-shaped members (belts and rollers) for an electrophotographic image forming apparatus.
2. Discussion of the Background
Various types of belt-shaped and roll-shaped members (belts and rollers) are used for an electrophotographic image forming apparatus. Recently, demands for electrophotographic full-color and high-quality image forming apparatus are increasing, and members for the apparatus are required to have high quality in accordance with the demands.
The belt-shaped member (hereinafter referred to as a belt) is a flexible, seamless and cylindrical member. A metallic electroconductive substrate being a member for a photoreceptor, a photoreceptor belt bearing a latent image and including at least a photosensitive layer, and a resin made transfer belt and feeding belt mainly used for forming a full-color image are used in practice. In addition, recently, a resin-made or a metallic belt-shaped fixing belt that fixes a transferred toner image on a copy paper is being developed. Further, the above-mentioned metallic electroconductive substrate is being applied to the feeding belt or the fixing belt.
The photoreceptor belt includes at least a photosensitive layer formed on the above-mentioned metallic electroconductive substrate and a sheet photoreceptor including at least a photosensitive layer formed on an electroconductive layer of a resin film including the layer, both ends of which are bonded by an ultrasonic wave, etc.
The roll-shaped member (hereinafter referred to as a roller) is a rigid cylinder or a cylindrical member. An electroconductive metallic tube, a photoreceptor drum including a photosensitive layer formed thereon, and a charging and developing roller including a (semi) electroconductive elastic layer coated on a surface of an electroconductive metallic axis, are used in practice. An organic semiconductor, selenium and an amorphous silicone, etc., are used as a material included in the photosensitive layer of the photoreceptor drum.
These members are commonly required to have surface smoothness. Some members have a convexity or a dotted convexity impairing their smoothness, and are regarded as poor-quality members. This is because electrophotographic image forming apparatuses having such members produce poor-quality images in many cases. Therefore, the convexity has to be detected, and such members as have a convexity beyond an acceptable tolerance for an electrophotographic image forming apparatus, have to be removed in a process of producing the members.
The above-mentioned convexity will be explained, referring to examples.
The electroconductive substrate is mainly formed of nickel, stainless steel, etc. A belt substrate made of the nickel is typically produced by an electroforming method, such as an electroforming method using a nickel sulfamate liquid. When there is a foreign particle or an abnormal separation of a crystal in the liquid, the resultant nickel coated surface occasionally has a convexity.
When a photosensitive layer forming liquid is coated on the nickel belt having the convexity, there is a coating defect on the convexity, and therefore, an image forming apparatus equipped with such a photoreceptor belt produces defective images.
Coating defects are inevitable by any coating method such as a dip coating method, a spray coating method or a nozzle coating method so long as the photoreceptor belt made of nickel has such a specific convexity in greater or lesser degrees.
As a resin film for use in the above-mentioned sheet photoreceptor that is one of the photoreceptor belts, e.g., when a stretched polyethyleneterephthalate film is used, a surface waviness caused by a nonuniform stretching or bonding of both ends of the film adverse effects performance of the resultant photoreceptor.
In addition, when a belt made of a resin such as polyimide used for the transfer, feeding or fixing belt is produced by an extruder, the belt occasionally has an uneven thickness or a surface waviness. When produced by a centrifuge, the belt occasionally has a protrusion or a surface waviness. When belts having such defects are used as members of an image forming apparatus, the apparatus produces poor quality images.
Further, various convexities are formed on a surface of rollers during production, as seen in the following explanation.
When a photoreceptor drum having an organic photosensitive layer formed by a dip coating method is produced, an end of the photosensitive layer occasionally has a bubble or protrusion.
In addition, a charging or developing roller produced by coating a (semi)conductive seamless tube on a surface of a conductive metallic axis occasionally has a wrinkle in its coating or includes air or a foreign particle therein.
Various methods of detecting such convexities present on a surface of a member included in an electrophotographic image forming apparatus have been suggested, and some of them are in practical use.
For example, Japanese Laid-Open Patent Publication No. 5-18728 discloses a method of uniformly irradiating a surface of a belt with light and detecting an image while projecting a fixed pattern to detect a distortion of the pattern. However, this method has a disadvantage of requiring an optical system (such as a lens, a CCD and an image processor), and sophisticated software making a decision to pass or fail a defect.
Japanese Laid-Open Patent Publication No. 62-189477 discloses a method of producing an image by an image forming apparatus including an amorphous silicon photoreceptor and actualizing a defect of the image to detect a spherical protrusion present on the photoreceptor. However, this is a complex method because an image forming apparatus equipped with the photoreceptor has to be set up and an image has to be produced to see. In addition, a causal relation between a defect of the image and a protrusion of the photoreceptor is uncertain, and detecting accuracy is doubtful.
Japanese Laid-Open Patent Publication No. 2000-214100 discloses an apparatus pressing a first roller against a surface of a second roller in parallel, and relatively scanning a surface of the first roller to detect a protrusion based on a displacement amount of the first roller. This method has a problem that it is difficult to detect a micro protrusion because the protrusion has to move the first roller, having a mass, to be detected. In addition, this method has another problem of misidentifying a dust particle as a protrusion when the dust particle adheres to the rollers because the dust causes displacement of the first roller. Therefore, this method requires a complete dust removal and has a disadvantage of enlarging the apparatus.
Various methods are suggested to detect a protrusion even in a field other than a field of production technology of the electrophotographic image forming apparatus.
Japanese Laid-Open Patent Publication No. 2000-258354 discloses a method of irradiating light having different colors to a printed matter from different three directions. However, since it is difficult to uniformly irradiate a whole surface at a time, an inspected area becomes a small spot. Therefore, the method requires time to scan this inspection spot over the whole surface. In addition, a moderate protrusion cannot sufficiently be detected.
Japanese Laid-Open Patent Publications Nos. 8-35939 and 9-33449 disclose a method of detecting a protrusion present on a surface of a textile fabric sheet using a CCD. However, this method requires an illuminating system and a CCD, which enlarges an apparatus and does not accurately detect a moderate protrusion although it effectively detects a micro-protrusion.
Japanese Laid-Open Patent Publication No. 8-5575 discloses a method of detecting a foreign particle protrusion and a detector optically separating the foreign particle protrusion from an adhered foreign particle of a color filter, and sorting out the foreign particle protrusion that is higher than an acceptable height. However, this apparatus is complicated because it requires a transportable stage producing a XY coordinate, a color filter, and a complicated optical system. In addition, the apparatus cannot accurately detect a moderate protrusion. Further, when dust adheres to the color filter, the apparatus occasionally misidentifies the dust as a protrusion. Therefore, complete dust removal is required before inspection, and the apparatus is enlarged.
Japanese Laid-Open Patent Publication No. 10-10277 discloses a method of detecting a protrusion on an inside surface of a cylinder. However, this method has a problem of taking time to scan a gauge head over the whole inside surface of the cylinder.
As mentioned above, various convexities are frequently formed on a surface of a belt or roller that is a member of an electrophotographic image forming apparatus, which convexities are caused by its production method and directly or indirectly cause deterioration of the resultant image quality. It is desirable that the convexity be detected, and a member having a convexity beyond an acceptable tolerance be removed.
Although various methods of detecting the convexity are in practical use and suggested, they often misidentify a dust particle as a convexity and cannot accurately detect a moderate convexity or a micro-protrusion. In addition, inspection time is long, and the apparatus is complicated or large, resulting in a high cost of the inspection.
Because of these reasons, a need exists for a detection method and apparatus easily and accurately detecting a convexity present on an inside and outside surface of a belt or roller at a low cost.